1. Technical Field
The present invention relates to light guide plates and liquid crystal display devices. Specifically, the present invention relates to a light guide plate used in a backlight or the like, and a liquid crystal display device in which the light guide plate is used in an area light source device such as a backlight.
2. Related Art
An area light source device used as a backlight of a liquid crystal panel is disclosed in Japanese Unexamined Patent Publication No. 2002-82625. The area light source device disclosed in Japanese Unexamined Patent Publication No. 2002-82625 is shown in FIG. 1.
In such an area light source device, a corner of a rectangular light guide plate 11 is cut diagonally or an edge of the light guide plate 11 is cut to a V-groove shape to form an inclined surface 12 that is diagonally inclined, and a light source 13 having high directivity is arranged to face each inclined surface 12. In Japanese Unexamined Patent Publication No. 2002-82625, such a configuration prevents a bright portion and a dark portion from alternately occurring at a surface of the light guide plate thereby causing luminance unevenness even when the light source having high directivity is used.
However, in the backlight (area light source device) used in the liquid crystal panel of a portable telephone or the like, the size and the aspect ratio of a light emitting surface differ depending on the individual model. Furthermore, the dimension of the light emitting surface actually generally differs by a little bit even with the light emitting surface size of the same type. (e.g., the dimension of the light emitting surface slightly differs depending on the model of the portable telephone even with the same size of three inches).
Thus, in the backlight of such an application, the dimension of the light guide plate and the arrangement of the light source needed to be optimized each time when designing the individual model when the light emitting surface size is different, of course, and also when the light emitting surface size is the same. When the arrangement of the light source changes, an optical pattern provided on the back surface of the light guide plate needed to be re-designed so that the light emitting luminance becomes even. Therefore, the design of the light guide plate needed to be redone with enormous cost and time when forming the backlight of different size.
Furthermore, since the light guide plate of the backlight is a resin molded article and is normally manufactured by injection molding, a dedicated molding die needs to be formed every time when the outer shape dimension of the light guide plate or the light emitting surface size is even slightly different. Furthermore, when newly forming the molding die, the density, shape, or the like of the optical pattern formed in the die piece of the back surface of the light guide plate needs to be adjusted each time so that an even light emitting luminance can be obtained. A great amount of trouble and time are thus required to form the die, and an enormous cost is also necessary.